Reconciliation of Basic to Diluted Shares Outstanding (Detail) - shares shares in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Schedule Of Weighted Average Number Of Diluted Shares Outstanding [Line Items]
Basic	192.7	200.1	210.7
Dilutive effect of shares issuable under stock-based compensation plans	2.7	3.3	4.0
Diluted	195.4	203.4	214.7
Antidilutive options to purchase common shares and restricted stock as well as contingently issuable restricted stock which are excluded from the table above	0.6	0.7	0.7